Au—Sn alloy solder paste is generally used in joining a substrate and semiconductor elements such as GaAs light elements, GaAs high frequency elements, and thermo-conducting elements, and in sealing of packages of fine and high-airtight requiring devices such as SAW filters and crystal oscillators. It is known that Au—Sn alloy powder included in the Au—Sn alloy solder paste is a powder of Au—Sn eutectic alloy having a composition containing 20 mass % of Sn with the balance consisting of Au and unavoidable impurities. It is also known that the Au—Sn eutectic alloy powder is generally obtained by a gas-atomizing process.
It is known that An-Sn alloy bump may be used as electrodes or the like by forming a perforated dry film layer on a substrate, filling the Au—Sn alloy paste in the perforations of the dry film layer, subjecting the Au—Sn alloy paste to reflow melting and forming Au—Sn alloy bumps on the surface of the substrate, and removing the dry film layer (see Non Patent Reference 1).    Non Patent Reference 1: Collected Papers of 10th Symposium on Microjoining and Assembly Technology in Electronics, Vol. 10, 2004, pp 95-100 (Published on Feb. 5, 2004 by Japan Welding Society)